Well, he knew she was the cleverest witch of her age. Of course she's figured him out. He lets the wheels turn, and-- he doesn't know how to answer the next question she doesn't answer for herself.

"The war ends October 31st, 1981..." Not quite the answer to her question, really, but stay with him. "Most people were convinced he'd been killed, for over a decade. But he-- came back, in June of 1995. And there was a second war, that ended in May, 1998. That's when it truly ended."

That's not getting into Delphini but-- well. Yeah. It's already complicated, and Lily Evans is clever enough to know wars don't end on a clean break.